The same way they end up where they want to go at all – They have a sense of the space around them before they actually move there. It varies how good angels are at this, though, so it’s not that unusual for them to bump into things or end up way off from their target destination. The halo does a lot of the work for you, but teleporting still Is magic that you wield yourself and requires practise (and talent) like any other type of magic.